As life standard advances, a lot of people enjoy watching movies and listening music using a home theater system at home. In order to implement a home theater system, as shown in FIG. 1, front left and right speakers, a sub-woofer, surround back speakers, surround left and right speakers and a center speaker are needed in order to build a surround sound along with a large size screen. Among the above speakers, a center speaker is disposed between the front left and right speakers for emphasizing the flow of sound for thereby achieving a perfect sound image. It is generally sound to output words while being disposed at the same position as the front left and right speakers. In addition, the center speaker is disposed closer to a television set (generally above or below the television set) at the heights of human ears. The center speaker can be called as a key speaker in the system.
The television monitor advances from a CRT to an OLED through LCD and PDP with the helps of a DVD, a HDTV and a digital air system. The screen sizes become larger and larger. When the surround environment is installed in a living room or a room, it is hard to properly arrange speakers. In case of the center speaker, it outputs words which are a lot contained in a movie not as an effect component channel, so the arrangement of the same is very important.
Since the center speaker is configured to clearly output words, a frequency response characteristic of the speaker is very important. The audio frequency AF that a human can hear is 20 through 20,000 Hz. The center frequency of a human voice mainly resides at 10,000 Hz. The person intends to recognize the direction of sound lower with respect to the frequency of below 10,000 Hz, and the direction of sound higher with respect to the frequency of above 10,000 Hz. So, the center speaker should be disposed at the center of the screen, but it is impossible to practically dispose the same at the center of the screen, so it is disposed below or above the television set instead. As a result, the above center speaker is not able to output a perfect sound field. However, in case of a theater, the center speaker can be installed behind the screen, so a perfect sound field effect can be obtained.
As the screen sizes become larger and larger, the center speaker is still disposed in the center of the screen. Even when the person who talks in a movie or something is positioned in the left side or the right side or in the upper side or the lower side, the words of the person in the movie are outputted only from the center of the screen, so it is impossible for a movie viewer to listen to balanced words.